1. Field of the Invention
This invention relates to an improvement of an electromagnetic induction heating device making use of an electromagnetic induction and an image recording device using such a heating device.
Here, the image recording device is of a type which transfers and fixes an unfixed image carried on an image carrying body to a recording member such as a paper or the like, and to be more specific, it widely includes an electrophotographic recording device, device, an electrostatic recording device, an ionography, and devices which performs forming of an image making use of a magnetic latent image.
2. Description of the Related Arts
Conventionally, this kind of electromagnetic induction heating device has been used as a fixing device of an image recording device.
As such a fixing device, a fixing device which makes the alternating magnetic fluxes of magnetic field generating unit applied to an electromagnetic induction exothermic or heat generating member (a heating roller) and so as to generate heat necessary for heating an unfixed toner image on a recording member such as a paper or the like has been known. The device includes an exciting coil and a magnetic material (core) as magnetic field generating unit, an exciting circuit for supplying electricity to an exciting coil and temperature control unit for controlling the temperature of the electromagnetic induction heat generating member by controlling an output of the exciting circuit (see Japanese laid-open patent publication Hei 10-301415, for example).
Furthermore, a technique in which a plurality of cores are arranged in parallel in a heating roller of the fixing device and an exciting coil is wound around each core so as to change a heat generating region in a rotating shaft direction of the heating roller has been already known (see Japanese laid-open patent publication Hei 7-319312, for example).
In this kind of fixing device, the size of the core must be set approximately corresponding to the maximum heat generating region, in principle, it is extremely difficult to prepare the core having a large size.
This is because that shrinkage percentage of the core is extremely large at the time of manufacturing the core by baking the core for 6 hours at a temperature of 1200.degree. C. after compacting and forming the ferrite powder usually and hence, the assurance of the accuracy of size around 100 mm or the maintenance of the flatness of the flat surface of rectangular parallelepiped having a square of 100 mm becomes extremely difficult.
Accordingly, there has been a technical problem that the distance between the core and the heating roller becomes irregular and hence, irregular heat generation occurs at the time of heating the heating roller.
To solve such a technical problem, in a mode where a plurality of cores are arranged, for example, it is considered that exciting circuits provided for respective exciting coils corresponding to respective cores are individually controlled. In this case, however, basically, the number of the exciting circuits must be equal to the number of the cores and hence, the construction of the control system becomes complicated. Furthermore, the control per se which performs a temperature control of the heating roller by correcting the irregularities of the distance between each core and heating roller becomes extremely cumbersome.
Furthermore, in the fixing device which constitutes this type of electromagnetic induction heating device, toner and a recording member are heated while being nipped together between the heating roller and a pressure roller which faces the heating roller in an opposed manner and hence, a noticeable reduction of the energy consumption cannot be obtained.
Still furthermore, the toner is heated at the pressure contact portion between the heating roller and the pressure roller and hence, the temperature of the toner in a fixing region, that is, in the vicinity of an exit of the pressure contact portion is elevated and hence, there is a technical problem that the offset is liable to occur.